Patent Literature 1 describes that “in a state where a driver is not operating a brake pedal, a rod with a thread groove is located at its most retracted position in a motor-driven cylinder, together with which each piston biased by its corresponding return spring is retracted, and no braking fluid pressure is generated in both fluid pressure generating chambers. When the brake pedal is stepped on and a detected value in a stroke sensor becomes greater than 0, a braking fluid pressure corresponding to a braking volume of the brake pedal (brake operation volume) as an input is generated in a first fluid pressure generating chamber, and at the same time a second piston is displaced against biasing force of the return spring by being pressed by the fluid pressure in the first fluid pressure generating chamber, and a braking fluid pressure is similarly generated in a second fluid pressure generating chamber as well”.
In a braking control device described in Patent Literature 1, the pistons are pressed to the most retracted positions (initial positions) by the return springs in the state where the brake pedal (brake operation member) is not operated. Further, when the brake pedal is stepped on, the pistons displace against the biasing force (spring force) of the return springs, and the braking fluid pressures are generated in the fluid pressure generating chambers. At this occasion, the pistons do not return to the initial positions easily if the spring force of the return spring is small, whereas in a case where the spring force of the return springs is large, large-sized electric motors to handle such spring force become necessary. That is, a trade-off relationship exists between the return springs and the size of the electric motors. A configuration that allows pistons to return to initial positions despite spring force of return springs being small is desired to make a braking control device compact.